Geochemical Characteristics And Petrogenesis Of The Erhongwa Mafic-Ultramafic Intrusion, Xinjiang

The Erhongwa mafic-ultramafic intrusion is at the western part of the Huangshanmafic-ultramafic rock belt which is located at the eastern part of the north Tianshan orogenicbelt, It develops a series of regional mafic-ultramafic rocks and highly concerned bygeologists. Xiangshan intrusion,Huangshan intrusion,Huangshandong intrusion,Huluintrusion,Tulaergen intrusion have magmatic sulphide deposits; Erhongwa intrusion andHuangshannan intrusion develops Ni-Cu sulphide mineralization. In recent years, manygeologists have done a lot of research on large deporsits of the Huangshan belt,compared toErhongwa intrusion. This paper study systematically Ehongwa mafic-ultramafic intrusionthrough research on the petrology, mineralogy, geochemical and isotope chronology etc,expounds the geological characteristics and the properties of magma source with originalmagma, and discusses magmatic evolution process and assimilation-hybridization. Based onthese researches, we get some understanding as follows:1. Erhongwa mafic-ultramafic intrusion is divided into two smaller intrusions whichnamed north and south intrusion, covered an area of1.42km~2and6.25km~2, respectively. TheErhongwa intrusion is composed of two intrusive rocks units, the first period haveplagioclase-bearing lherzolite and olivine gabbro, and the second period which is composedof gabbronorite and leucogabbro. The main rock-forming minerals are olivine, pyroxene andplagioclase.2. The study of petrography，petrochemistry and crystal chemistry of minerals suggestthat The m/f values of rocks range from2.31to5.02,so Erhongwa mafic-ultramafic intrusionbelong to ferruginous rocks.The concentrations of rare earth elements is very low,the light areearth elements，are weak.The diragram of trace element which normalized by primitive mantledemonstrate that most of the rocks are enriched in Ba、Th and show negative Nb-Taanomalies.3.It can be obtained the MgO content of primitive mantle through the Fo molecular ofolivine in Erhongwa mafic-ultramafic intrusion is15.73%, and the parental magma of theErhongwa mafic-ultramafic intrusion was a picritic magma.But Fo value(89.7) is not highenough to represent the balance of the original magma liquidus initial phase,so15.73%ofMgO content can only bond its lower limit.4. Hf-Sr-Nd isotopic characteristics indicate that Erhongwa mafic-ultramafic intrusioncomes from depleted mantle source, the parental magma was formed by a depletedmantle-derived magma with7-32%of the A-type granitic melt at depth followed by <5% assimilation of the upper crust at shallower levels.5. The results of La-ICP-MS zircon U-Pb date shows that the age of olivine gabbro is283±1.5Ma,almost is coeval with Xiangshan intrusion,Huangshan intrusion,Huangshandongintrusion,Hulu intrusion,Tulaergen intrusion of the Huangshan mafic-ultramafic rock belt. Thestudy of petrography，petrochemistry and crystal chemistry of minerals suggest that parentalmagma of Erhongwa intrusion undergone fractional crystallization of olivine,orthopyroxene,clinopyroxene and plagioclase.6. Erhongwa mafic-ultramafic intrusion is formed in eaely Permain under thebackground of post-collisional extension setting in east Tianshan.